Archive:
Arctic Climate

A new study[1] finds that the snow albedo feedback by snow grain growth alone is insufficient to explain the observed decrease in the springtime Greenland ice sheet reflectivity. They propose a theory that “recent warming in the Arctic has induced an earlier disappearance of the seasonal snow cover, uncovering large areas of bare soil and thus enhancing dust erosion”. The vigorous late winter wind would take the dust to Greenland.

Year 2014 Greenland upper elevations ice reflectivity has been at record low values much of 2014 so far, and in recent years, consistent with the conclusions of Dumont et al. (2014). See the blue line; year 2014.

Year 2014 Greenland upper elevations ice reflectivity has been at record low values much of 2014 so far, consistent with the conclusions of Dumont et al. (2014) for recent years. See the blue line (year 2014) in March.

2014 is on track for a big melt year at the upper elevations. What could shut this down would be heavy snowfall there. For the ice sheet as a whole, 2014 reflectivity has been trending near the low side of past observations since 2000. Is this the early spring dust factor? More springtime dust certainly is a factor. What will determine how much punch the 2014 melt season delivers depends a lot on temperatures and atmospheric circulation in the month of June. Here we go.

What’s been driving the low reflectivity anomaly for the ice sheet the past 10 days is melting concentrated along the southeast ice sheet. Note the red areas below.

Greenland ice albedo anomaly we are posting at polarportal.dk. Note the red, orange and yellow areas along the southeast ice sheet. The melt story so far for June is the southeast. It’s been since 2006 that this was the high melt story.

I’m today on my way to Greenland, to the western ice sheet, to camp there in the blue area of the map where there appears to be above average snow depth, contributing to the positive reflectivity anomaly. We may well have to put the camp in at a lower elevation where melt is more advanced because this extra half meter of melting snow, a.k.a. slush would be most unpleasant to camp in/on. Wish us luck.

“There’s so much pollution in the air now that if it weren’t for our lungs, there’d be no place to put it all.”

Robert Orben, 1927

The dawn of the industrial revolution, in the 18th century, marked the beginning of a dramatic change in the impact that humans have on the Earth. Smoke relentlessly billowed from factories, day and night, to keep up with the ever-increasing demands on growing industries such as agriculture and textiles. By the 1850s, a secondary revolution was spurred on by technological and economic progress as a result of steam-powered ships and railways. These efforts climaxed in the mid-19th century with the momentous invention of the internal combustion engine and the generation of electricity.

“It was a town of red brick, or of brick that would have been red if the smoke and ashes had allowed it; but as matters stood, it was a town of unnatural red and black like the painted face of a savage. It was a town of machinery and tall chimneys, out of which interminable serpents of smoke trailed themselves for ever and ever, and never got uncoiled. It had a black canal in it, and a river that ran purple with ill-smelling dye, and vast piles of building full of windows where there was a rattling and a trembling all day long, and where the piston of the steam-engine worked monotonously up and down, like the head of an elephant in a state of melancholy madness….”

Of course, the abundance of smoke generated during this new mechanical era didn’t just disappear into thin air. Instead, air pollution from the burning of fossil fuels had (and has) a consequential effect on the balance of the Earth’s elements. One element that has sparked interest within the Dark Snow Project is nitrogen. When fossil fuels are burned, reactive nitrogen, in the form of nitrogen oxides (NO and NO2, referred to collectively as NOX), are expelled into the atmosphere. It is these gases that can ultimately form smog and acid rain. NOX is predominantly removed from the atmosphere through the production of nitrate (Geng et al 2014). In addition to this, a second major and historic source of human generated nitrate has come from chemical fertilizers; used to assist with the ever-increasing demands on our food resources due to our growing population. These nitrogen-based compounds have been sprayed onto our fields since the advent of the Haber Bosch process (an energy demanding reaction that enables fertilizers to be synthesized) in the early 20th century (Felix and Elliott 2013). Nitrate from farmlands can become aerolised into the atmosphere, and as a result, in addition to the increased burning of fossil fuels throughout the industrial revolution, the use of fertilizers further exasperated the generation of man-made nitrate sources.

So, if all this industrial and agricultural pollution started to occur over 200 years ago, how can we possibly know about it today? Well, once aerosolized, nitrate and NOX are transported by winds through the atmosphere until they are eventually deposited onto the Earth’s surface. Depositions that occur over the Greenland ice sheet actually become encapsulated in time, buried under layer upon layer of snow. Ice core scientists can then drill out an ice core and obtain a nifty geochemical history lesson that can span thousands of years.

Human impacts on the nitrogen cycle (Galloway et al 2008) can be detected through the use of stable isotopes (variations in the atomic mass of elements due to differing numbers of neutrons within an atom’s nucleus). 14N is the natural and most common form of the stable nitrogen element, making up over 99% of the molecules that we measure on earth. However, reductions in the rarer second form of nitrogen, 15N, has been linked to increases in human-generated NOX levels; and so has become a proxy for the impact of our fuel consumption and agricultural activities on the global nitrogen cycle (e.g. Felix and Elliott 2013, Geng et al 2014, Hastings et al 2009).

Graph by Geng et al (2014) depicting how increases in ice core nitrate levels are coupled with a decrease in 15N concentrations.

With the historic global increases of nitrate concentrations in mind, and predictions that these levels will continue to rise (Liao et al 2006), this year’s Dark Snow Project participants plan to take on an alter ego as farmers, and actually fertilize the surface of the Greenland ice sheet! The idea is to add our own sources of nitrate within fertilization plots, so that we can observe the impact that nitrate elevations have on the microbial communities of surface ice. In addition, we will be looking into the implications that changes in the microbial communities have on the lowering the surface albedo, and of course, ultimately enhancing ice sheet melt rates.

Dr Karen Cameron is a microbial ecologist working in the Department of Geochemistry at the Geological Survey of Denmark and Greenland. Her previous research has focused on biogeochemical interactions that occur within supraglacial and subglacial environments, and on the biogeographical variability of glacial associated microbial communities.

Works Cited

Felix J D and Elliott E M 2013 The agricultural history of human?nitrogen interactions as recorded in ice core 15N?NO3?Geophysical Research Letters 40 1642-1646

The study, in Proceedings to the National Academy of Sciences (Keegan et al. 2014) finds that black carbon from wildfires facilitated widespread Greenland ice sheet surface melting in just two years since the end of the 19th century: 1889 and 2012. They argue convincingly that not just warm temperatures, but the positive feedback with black carbon and surface solar heating can push the surface energy balance into net heating and ice melt. Further, the likelihood for future increases in air temperature and wildfire boosts the probability of high altitude former “dry snow area” surface melting by end of century to every few years, if not even more frequently, they conclude.

Dark Snow Project

The Dark Snow Project’s first goal was sampling of the 2012 summer melt layer to answer if and by how much black carbon from wildfire and industrial sources played an important role in the widespread 2012 July surface melting of the Greenland ice sheet.

After a successful crowd funding campaign, on 8 July, 2013 at the southern Greenland ice sheet topographic divide, we extracted several snow/ice cores through the 2012 melt layer as part of ‘lean and mean’ helicopter mission. Frozen samples were then transported to the Snow Optic Laboratory at NASA’s Jet Propulsion Laboratory where McKenzie Skiles, present at the coring, painstakingly measured the black carbon concentrations.

We find black carbon concentrations equivalent with the peak values in Keegan et al. (2104), around 14 parts per billion (equivalent with nano grams per gram). We had 3 samples with concentrations above 12 ppb.

We’re gearing up for a June-August 2014 intensive field campaign designed to further this science. In addition to continued investigation of black carbon, we are bringing new focus to analyze the darkening effect of microbes. Glacier and ice sheet biologist Dr. Marek Stibal will be gathering data on the increasingly pronounced effects of microbial and algal growth on the warming ice sheet.

As larger and larger ares of Greenland become subject to summer melt, more liquid water, a key limiting factor for microbial growth, is available on the ice sheet. In addition, Dr. Stibal and Dr. Karen Cameron will be examining whether fertilizing factors, such as nitrous oxide from industrial processes, may be encouraging additional biological activity on the ice sheet.

In a recent Dark Snow posting, Dr. Stibal noted that organisms on the ice produce dark pigments to shield themselves from intense sun, as well as other functions.

it is a sunscreen, a protection against the harmful UV radiation and also excessive visible radiation which can inhibit photosynthesis in the cells. But that’s not all. The pigment may also represent a sink for surplus energy that cannot be invested in cells due to limitations in temperature or nutrient availability, and may even act as a chemical defense against grazers as, for example, phenolic compounds in marine kelp. So, given the nuisances you have to put up with as an alga living on the surface of an ice sheet, it seems like a very useful thing to have.

Recent published science makes ever clearer that sea level rise from melting ice sheets will become a critical impact of climate change sooner than was imagined just a few years ago. In that light, the continuing research of Dark Snow Project to quantify additional contributing factors has never been more important.

Greenland contains the largest continuous mass of ice in the northern hemisphere; an area over 2 million km2. The frequency of Greenland surface melting has increased, likely as a result of human-induced climate warming, with the melt-area covering almost the entire ice sheet surface in 2012 (Ngheim et al. 2012; Box et al, 2013; Tedesco et al. 2013).

Ablation zone extent on the Greenland ice sheet: July 8 (left) and July 12 (right). On July 8, ~40% of the ice sheet was melting. Four days later, ~97% of the ice sheet surface had thawed. Credit: Nicolo E. DiGirolamo, SSAI/NASA GSFC, and Jesse Allen, NASA Earth Observatory

Although its fair to say that higher temperatures mean more melt, the response of earth’s glaciers and ice sheets to climate warming is complex, also depending upon a range of feedbacks (e.g. Box et al, 2012). For example, when ice melts, liquid water runs over its surface, sometimes collecting in pools and lakes. Liquid water is a more effective absorber of sunlight than snow or ice, so the overall reflectivity (also called albedo, Greek for ‘whiteness’) of the ice decreases. The result is faster ice melt. Melting promotes more melting.

Not only melt water that reduces Greenland ice sheet albedo. A variety of aerosol ‘impurities’ further reduce surface albedo. These include black carbon (BC) derived from incomplete combustion of fossil fuels, other industrial activity, biomass burning, and wildfire. Black carbon can be transported across the hemisphere through the atmosphere and deposited on ice, and currently the impacts remain uncertain (Hodson, 2014). Dark Snow field science is examining this question in detail based on 2013 field measurements and planned measurements for June-August, 2014.

The presence of microbes on the ice surface also alter albedo and can therefore influence melt rates (Yallop et al, 2012). They do so by growing and adding dark biomass to the ice, causing mineral fragments to aggregate and resist removal (flushing) by melt water, and by producing dark humic substances and pigments. There may even be a relationship between microbial activity and BC. Yet, it is not yet known whether microbes metabolise BC and reduce its impact, or cause it to “stick” to the ice surface and prevent its removal by flushing (Hodson, 2014).

Many microbes on the Greenland ice sheet inhabit ‘cryoconite’ holes; cylindrical tubes ‘drilled’ into the bright ice surface ice by dark cryoconite debris. The debris is a loose bonding of minerals encased in microbial biomass (e.g. Gribbon, 1979; Cook et al, 2010). Cryoconite holes on the Greenland ice sheet likely provide favourable conditions for photosynthesis by: 1.) maintaining light intensities that are high but not harmful because ultraviolet radiation is not transmitted by water; 2.) providing nutrients in melt water flowing in through the hole walls; and 3.) providing relatively long term (years) storage of microbes. This also promotes proliferation of bacteria and “grazers” that feed upon other microbes. These factors make cryoconite holes active and biodiverse ice sheet habitats (Hodson et al, 2008).

Cryoconite holes – generally considered to be the most biodiverse microbial habitats on glacier surfaces (photo, J. Cook)

Despite being the most studied biological entity on the surface of the Greenland ice sheet, cryoconite holes remain poorly understood in terms of their biological community dynamics, thermodynamics, evolution and impact on albedo. Further, the characteristics of the holes themselves, and the microbes inhabiting them, have been shown to vary depending upon location on the ice sheet (Stibal et al, 2012), and these spatial patterns probably also evolve over time. Edwards et al (2014) recently found microbial communities to be extremely dynamic in response to environmental change, while Irvine-Fynn and Edwards (2014) showed that hydrological and glaciological processes might also influence microbial activity. Cryoconite holes will provide research foci for some members of the field team in summer 2014. For further information on cryoconite, see: here; here; and here.

Dr Joseph Cook is a Lecturer in Earth and Environmental Sciences at the University of Derby (UK) who is particularly interested in researching the links between biological and physical processes on glaciers and ice sheets. He completed his PhD at the University of Sheffield (UK) in 2012 and has undertaken several Arctic field seasons. He is also an avid rock climber and mountaineer and maintains a cryosphere-focussed website (http://tothepoles.wordpress.com).

I updated my calculation of running 5-day temperature anomalies versus the same 5-day period for the ‘climate normal’ (a.k.a. most recent 30 year period beginning on a “1” year) 1981-2010. These data are from the US NCEP NCAR Reanalysis mixture of observations from satellites, ground stations, aircraft and numerical modeling.

Most striking to me is the Arctic Ocean area persisting warm…

The most recent map (that does not include forecast data) has the warm anomaly along the US west coast turned to cold anomaly. So, the whole US is in the cold in the most recent 5 day average. The warmest temperatures over the Arctic Ocean are 17 C above the 1981-2010 average for this 5 day period.

Here’s the situation over the US for the region bounded by 70 to 105 longitude west and 38 to 55 latitude north…